Solid propellant technology has evolved around the use of components readily available at the time of development and use. The surplus materials following World War II included gun powder, nitrocellulose, and other explosive ingredients. The availability of these materials motivated research for their use in solid propulsion technology. As these materials were used in solid propellants, the need for stabilizers was recognized. When stabilizers are used then a need is established for determining their change to ascertain the efficiency in stabilizing the propellant composition.
A patent of interest in the stabilizer technology field which is assigned to the United States of America as represented by the Secretary of the Army is U.S. Pat. No. 3,335,185. This patent was issued to Hiram W. H. Dykes on Aug. 8, 1967 and relates specifically to recovery of stabilizers such as diphenylamine and resorcinol. In the method disclosed by this patent a small propellant sample (e.g., 100 mg.) is first dissolved in a suitable inert organic solvent having a low boiling point, acetone being preferred. The separation of the stabilizers is accomplished by specific materials known as developers in a thin-layer chromatography method. The developers are selected from the normal eluotropic series which is generally made up of a listing of solvents ranging from low polarity to high polarity. The developers are selected from the group consisting of n-hexane, carbon disulfide, carbon tetrachloride, trichloroethylene, toluene, benzene, methylene chloride, chloroform, ether, ethyl acetate, methyl acetate, aceton, n-propyl alcohol, ethyl alcohol, methyl alcohol and water.
Although the above method serves to separate and identify specific ingredients in small amounts, the separation and reclamation of massive amounts of propellant ingredients has not been of major concern since, prior to the use of very expensive specialty ingredients, the normal disposal of of hazardous munitions and ingredients centered around open burning and open destruction (OB/OD). However, after environmental controls were implemented, and with expectation of further controls in the future, the need for a different approach for demilitarization and disposal of surplus and reject propellants, explosives, and energetic materials has become a major driving force.
The advancements of new technologies relating to propellant processing and reclamation of special ingredients from propellants highly loaded with particulate solids are disclosed in my co-inventions as follows:
a. Statutory Invention Registration, Reg. Number H273, published on May 5, 1987, discloses "Processing of High Solid Propellant" by William S. Melvin and Porter H. Mitchell. This process relates to mixing of high solids loaded composite propellants at reduced viscosity by employing near critical liquid (NCL) carbon dioxide as a carrier fluid in a volume amount from about 10 to about 20 percent of the volume of the propellant ingredients. A typical composite propellant contains about 88 percent solids by weight, comprised of ammonium perchlorate, aluminum powder, ballistic modifiers, bonding agent, and about 12 percent liquid ingredients by weight, comprised of liquid polymers, plasticizers, and curatives.
b. Statutory Invention Registration, Reg. Number H305, published on July 7, 1987, discloses "Demilitarization of High Burn Rate Propellant containing Ferrocene or its Derivatives" by William S. Melvin and Porter Mitchell. This invention accomplishes removal of about 99.8% to 100% of ferrocene or its derivatives (e.g. Catocene) from composite propellant which is undergoing demilitarization. After recovery of the high dollar value catalyst material, the propellant can be safely handled during further processing using conventional water jet apparatus to cut and remove the propellant from a rocket motor case, for example, after which reclamation of other specific propellant ingredients can take place.
c. U.S. Pat. No. 4,854,982, issued on Aug. 8, 1989, discloses "Method to Demilitarize, Extract, and Recover Ammonium Perchlorate from Composite Propellants Using Liquid Ammonia" by William S. Melvin and James F. Graham. This method removes substantially 100% of the ammonium perchorate from composite propellant in high purity. When large rocket booster units employing thousands of pounds of composite propellant are required to be demilitarized, an environmentally acceptable method is now available to recover a marketable product, ammonium perchlorate oxidizer, from the surplus propellant. This method recycles ammonia following extraction of the ammonium perchlorate from the propellant. Recovering the ammonium perchlorate from the liquid ammonia during liquid-gas phase change is accomplished via a process whereby ammonium perchlorate oxidizer is released in predetermined particle sizes based on liquid droplet sizes and rate of pressure change at a specified temperature. Following this phase change for recovering the ammonium perchlorate, the gaseous ammonia is dried and compressed to liquid ammonia.
The above extensive review of background information teaches that great progress has been made in the demilitarization of composite propellant compositions. There remains a need for a similar process for another type of propellant which contains nitrocellulose and plasticizers therefor. It is recognized that this type of propellant, which is used in certain missiles and explosive, fall into the category disclosed in U.S. Pat. No. 3,711,344 which was issued on Jan. 16, 1973 to Everette M. Pierce and assigned to the United States of America. For these propellants, which are briefly described hereinbelow, there is also a need for a demilitarization or extraction method which can extract special ingredients from them on a large scale by an environmentally acceptable method. Such a method would satisfy a major requirement in the propellant industry.
The extraction and recovery method of this invention is useful with nitrocellulose-based propellants wherein nitrocellulose is a substantial ingredient. These propellants include components wherein the nitrocellulose source ingredient (whether minor portion or major portion of a nitrocellulose source ingredient) is double-base powder (e. g., contains nitrocellulose, nitroglycerine, and stabilizer), single-base powder (e.g., contains only nitrocellulose and optional stabilizer), or plastisol grade nitrocellulose, all of which are commercially available and well known in the processing art.
The term "plastisol nitrocellulose" (PNC) propellant is used to described double-base propellants made by slurry mixing and pouring incured propellant into casting molds or rocket motors. PNC propellants are made using ball powder (single or double-base) or plastisol grade nitrocellulose. PNC propellants, when freshly mixed, are fluid and free-flowing, usually less than one kilopoise in viscosity at room temperature.
Processing of crosslinked nitrocellulose propellants and crosslinked plastisol nitrocellulose (XL-PNC) involves mixing and heating the selected propellant ingredients (except the second and major portion of the nitrocellulose source ingredient plus a suitable amount of crosslinker), so that any residual moisture will react with a first portion of an isocyanate. Heating above 85.degree. F. and within a range of temperature from about 85.degree. F. to about 140.degree. F. is preferred. Water and isocyanates react to release carbon dioxide which in turn causes cracks and voids in the cured propellant unless the carbon dioxide is removed from the propellant before casting.
In addition to the nitrocellulose, the other ingredients of a basic propellant mix which can be processed by the process of the above patent includes a plasticizer, stabilizer, and crosslinker. Metal fuel and organic or inorganic oxidizers may be used. The propellant mix may contain one plasticizer compound or the mix may contain two or more plasticizer compounds as disclosed hereinbelow.
The compositional range of propellant grains which can be produced by the process of the above patent can vary greatly, but generally, the ranges of ingredients in the final propellant composition, in percents by weight, are nitrocellulose 5-25, plasticizers 20-60, metal fuel 0-30, oxidizer 0-70, stabilizer 1-2, and crosslinker 0.2-3%.
Most of the conventional propellant ingredients can be used in crosslinked double base propellants. Oxidizers such as ammonium perchlorate, ammonium nitrate, potassium perchlorate, nitronium perchlorate, cyclotetramethylenetetranitramine (HMX), and cyclotrimethylenetrinitramine (RDX) can be used. Metal fuels such as aluminum, zirconium, boron, beryllium, and magnesium can be used.
Plasticizers which can be used are of two types: the energetic or explosive type such as nitroglycerin, butane trioltrinitrate (BTTN), diethylene glycol dinitrate (DEGDN), triethylene glycol dinitrate (TEGDN), trimethylolethane trinitrate (TMETN), and tetraethylene glycol dinitrate (TEGDN), and the inert or non-explosvie type such as triacetin, diethyl phthalate, propyl adipate, and dibutyl sebacate.
Stabilizers are used to stabilize the nitrocellulose and nitrate ester plasticizers during cure and storage. Resorcinal, p-nitro N-methyl aniline, and 2-nitrodiphenylamine are typical stabilizers. Resorcinol, a good stabilizer, is also a colloiding agent for nitrocellulose which helps improve the mechanical properties of XL-PNC propellants.
The diisocyanates (crosslinkers) used have included toluene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and a prepolymer of polyglycol adipate-toluene diisocyanate (PGA-TDI).
The following ranges for two crosslinked nitrocellulose compositions which are taught in U.S. Pat. No. 3,711,344 include: double-base powder 12.0-16.0, TEGDN 28.0-35.0, BTTN 16.0-0.0, HMX 40.0-0.0 aluminum 0.0-15.0, ammonium perchlorate 0.0-30.0, resorcinol 1.0-1.0, ethylenediamine (EDI, added) 1.0-1.0, and ballistic modifier 3.0-3.0.
The desirability of a method to extract and recover plasticizers from solid propellants, in accordance with recent Environmental Protection Agency (EPA) restrictions limiting OB/OD of hazardous wastes and munitions, is readily recognized as touching all phases of the propulsion and explosives industries. This is based on the fact that civilian Government agencies, such as NASA, as well as DOD and its contractors now experience the impact of these new regulations on the demilitarization of high energy propellants, explosives, and pyrotechnics, commonly referred to as PEP compositions or PEP ingredients.